LC 2. 两数相加

代码 :

class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        auto dummy = new ListNode(-1); 
        auto ptr = dummy;
        int carry = 0;
        while(l1 || l2) {
            int num1 = l1 != NULL ? l1->val : 0;
            int num2 = l2 != NULL ? l2->val : 0;
            int sum = num1 + num2 + carry; 
            ptr->next = new ListNode(sum % 10);
            ptr = ptr->next;
            carry = sum / 10;
            if(l1) l1 = l1->next;
            if(l2) l2 = l2->next;
        }
        if(carry) 
            ptr->next = new ListNode(1);
        return dummy->next;
    }
};